The 20-year-old has a superior arm; he’s quicker and can cover more ground.

This was evident during spring training…Castro’s a fielding web-gem…Theriot, not so much.

But Theriot, however, remains the better fielder…why is that?

Simple really…fielding is all about consistency…making the routine plays…turning tailor made double plays…and understanding situational baseball.

All of this prevents runs from scoring…and Theriot’s mastered that principle…despite his athletic shortcomings.

Castro, of course, is learning on the job…and at the top level of all places. Yes, he’s superbly talented, but his three errors Monday night…all on routine grounders…shows his consistency remains a work in progress.

Still, you can’t blame kid…he’s been rushed to the show…thrust into the spotlight and saddled with the burden of sparking a veteran club…a club that’s performed so badly Castro was summoned from Double-A ball in the first place.

With the Cubs’ continuous struggles offensively, it makes sense to move Theriot to second base…Castro makes Chicago stronger up the middle…they’ll allow fewer runs…and perhaps, muster enough offense to win a few games.

But the real question isn’t whether Castro is a defensive wiz, but rather…can he make enough routine plays to save the Cubs’ season?